This chapter started by explaining the Unix design philosophy, including the central principles or pillars of the Unix philosophy, design, and architecture. We then described the Linux system architecture, where we covered the meaning of CPU-ABI (Application Binary Interface), ISA, and toolchain (using objdump to disassemble a simple program, and accessing CPU registers with inline assembly). CPU privilege levels and their importance in the modern OS were discussed, leading in to the Linux system architecture layers – application, libraries, system calls, and the kernel. The chapter finished with a discussion on how Linux is a monolithic OS and then explored kernel execution contexts.
In the next chapter, the reader will delve into the mysteries of, and get a solid grasp of, virtual memory – what exactly it means, why it's in all modern OSes, and the key benefits it provides. We will discuss relevant details of the making of process virtual address space.